With increasing development of communication technologies, handheld communication apparatuses such as mobile phones become essential communication products because they are portable and convenient. Recently, a variety of new mobile phones are brought forth and the old ones are weeded out soon. For increasing competitiveness of these mobile phones, the general trends in designing information electronic devices are toward small size, light weightiness and easy portability. Generally, either slim-type injection molding of plastic material or minimization of the electronic components are redered for facilitating fabrication of slim mobile phones.
As known, electrostatic discharge and electromagnetic interference (EMI) are detrimental to the electronic components on the circuit board inside the communication products. For a purpose of minimizing the influence of electrostatic discharge and/or electromagnetic interference (EMI), some important electronic components should be shielded by electrically conductive material, which is referred hereinafter as EMI shielding case.
Conventionally, the EMI shielding case is welded to a ground wire on a printed circuit board (PCB) of the handheld communication apparatus according to the surface mount technology (SMT). Before the EMI shielding case is welded to the ground wire, solder paste has been previously coated onto the circuit board and a steel plate should have been washed. As a consequence, the process of assembling the EMI shielding case is complicated and labor-intensive. Moreover, for maintaining the electronic components which are shielded by the EMI shielding case, the whole EMI shielding case should be detached for inspecting or replacing the shielded electronic components. In addition, the height of the EMI shielding case with respect to the surface of the circuit board is not small enough.
Generally, the conventional EMI shielding cases are classified into two types, i.e. a one-piece structure and a two-piece structure, which are illustrated as follows with reference to FIGS. 1 and 2.
Please refer to FIG. 1, which is a schematic cross-sectional view illustrating a one-piece structure of an EMI shielding case. In FIG. 1, the EMI shielding case 11 is directly welded to a ground wire 121 of a printed circuit board 12 according to the surface mount technology (SMT), thereby shielding the electronic components 13. For neat drawings, however, only one electronic component is shown in the drawing. As previously described, since the EMI shielding case should be detached from the printed circuit board 12 for inspecting or replacing the shielded electronic components, it is time-consuming and labor-intensive to maintain the electronic components shielded by the one-piece EMI shielding case 11. In a case that this EMI shielding case 11 is detached from the printed circuit board 12, it fails to be repeatedly used because it is likely distorted. In addition, during the EMI shielding case 11 is detached from the printed circuit board 12, the electronic components next to the EMI shielding case 11 are possibly collided with the EMI shielding case 11.
Please refer to FIG. 2, which is a schematic cross-sectional view illustrating a two-piece structure. In FIG. 2, the two-piece structure comprises a shielding frame 21 and an EMI shielding case 22. Firstly, the shielding frame 21 is welded to a ground wire 231 of a printed circuit board 23 to enclose the electronic components 24 according to the surface mount technology (SMT). For neat drawings, however, only one electronic component is shown in the drawing. Subsequently, the EMI shielding case 22 is secured to the shielding frame 21 and thus the electronic component 24 is shielded by the EMI shielding case 22. In comparison with the one-piece structure, the two-piece structure is advantageous for maintenance because the EMI shielding case 22 can be separately detached from the shielding frame 21. Unfortunately, this EMI shielding case 22 is still likely distorted and thus fails to be repeatedly used.
In addition to the conventional one-piece structure and two-piece structure, a new approach for assembling the EMI shielding case is illustrated with reference to FIG. 3. The EMI shielding case 31 is referred as a contact-type EMI shielding case and comprises a shielding case main body 311, a metallic frame 312 and an elastic sheet 313. The metallic frame 312 and the elastic sheet 313 are substantially a one-piece structure by punching a metallic part. Firstly, the elastic sheet 313 is placed on a ground wire 321 of a printed circuit board 32 to enclose the electronic components 33. For neat drawings, however, only one electronic component is shown in the drawing. Then, the shielding case main body 311 and the metallic frame 312 are secured to the printed circuit board 32 by for example screwing or other fastening means. Due to the restoring force generated from the compressed elastic sheet 313, a firm attachment between the EMI shielding case 31 and the printed circuit board 32 is rendered. Moreover, the electronic components 33 can be mounted on several regions of the printed circuit board 32, which are partitioned by the metallic frame 312. Since the electronic components shielded by different regions are not interfered with each other, the overall EMI shielding effect is enhanced.
This approach is also advantageous when the maintenance of the shielded electronic components is required. Under this circumstance, the shielding case main body 311 is directly detached from the printed circuit board 32 by loosening the screws. Although the new approach for assembling the EMI shielding case is very convenient, there are still some disadvantages. For example, the width of the ground wire 321 should be at least 1.0 mm, which is much larger than that required for the one-piece structure or two-piece structure (e.g. 0.5 mm). That is to say, this approach for assembling the EMI shielding case will occupy much area of the printed circuit board 32.
In views of the above-described disadvantages resulted from the conventional method, the applicant keeps on carving unflaggingly to develop a shielding case structure of a handheld communication apparatus according to the present invention through wholehearted experience and research.